Sulphide ores of copper-nickel-cobalt are normally treated by multi-stage crushing, grinding and flotation to produce separate copper and nickel-cobalt concentrates that may then be smelted. A wide variety of mineral processing procedures can be used to separate the copper and nickel containing minerals, such as chalcopyrite (CuFeS2), cubanite (CuFe2S3), pentlandite (Ni4.5Fe4.5S8) and pyrrhotite (Fe7S8) which are typically present in copper-nickel-cobalt-precious metal sulphide ores.
A typical grade of copper concentrate would be 25-35% Cu. If the grade of copper is low (for example less than 25% Cu) then the concentrate may be less desirable and may incur higher costs for smelting or alternately may not be accepted by smelters. It is thus generally desirable to maximize the grade of copper in the copper concentrate, and accordingly to produce copper concentrates having relatively low levels of nickel and cobalt. Elevated levels of nickel in copper concentrates, for example in the range of 0.2 to 1.0% Ni, may adversely impact copper anode refining processes. High levels of nickel in the copper anode may for example cause anode passivation during refining. In addition, nickel contained in copper concentrates is often not paid for by copper smelters.
Similarly, in the production of a nickel sulphide concentrates for nickel smelting, a minimum grade of at least 4% Ni is generally desirable, and higher Ni levels are often attractive. The Cu content of nickel concentrates may be significant, but generally it is desirable to have a Cu content less than that of Ni.
There are a very wide range of options for hydrometallurgical treatment of copper concentrates to extract metal values, including the Activox™ Process, the Albion™ Process, the CESL™ Process, the BIOCOP™ Process, the MINTEK-Bactech™ Biological Leaching Process, the Anglo American Corporation—University of British Columbia Process, the Galvanox™ Process, the Total Pressure Oxidation Process, the Dynatec™ Process and the PLATSOL™ process (Dreisinger, 2006). A number of chloride based processes are also available, including the INTEC™ Copper Process, the Outotec™ Hydrocopper Process and the Sumitomo Copper Process. These processes are generally adapted to leach copper and other metals (such as nickel, cobalt and zinc) from a sulphide ore or concentrate feed materials. The metals that are leached may then be recovered from solution using a wide range of downstream technologies for metal separation and recovery (for example solvent extraction and electrowinning of copper, nickel and cobalt). A similarly wide range of technologies is available for hydrometalurgical treatment of nickel sulphide concentrates, which may be adapted to dissolve nickel and associated metals from the sulphide ore or concentrate, to be followed by separation and recovery of individual metals.
U.S. Pat. No. 6,315,812 provides an example of hydrometalurgical processes for the treatment of ores or concentrates, and is a useful illustration of a process that may be appropriate for concentrates containing significant precious metal values, the PLATSOL™ process.
The PLATSOL™ process may be adapted to provide a one-step treatment of mixed copper-nickel-cobalt-platinum-palladium-gold concentrates, using total pressure oxidation in the presence of a halide salt (eg. sodium chloride). The chemistry of the PLATSOL™ process can be divided into the main chemistry of sulphide mineral oxidation and the minor (but economically significant) chemistry of precious metal extraction. The mineral forms of copper, iron, nickel, cobalt and precious metals may be complex and varied, depending on the genesis of the natural ore source. In a purely illustrative example, subjecting a concentrate to PLATSOL™ leaching may be understood to dissolve copper, nickel and cobalt, as the soluble metal sulphate salts, and platinum, palladium and gold as the chloro-complexed species, as shown below.
Sulfide Mineral Oxidation for Base Metal ExtractionCuFeS2+4.25O2+H2O=CuSO4+0.5Fe2O3+H2SO4 FeS2+3.75O2+2H2O=0.5Fe2O3+2H2SO4 Fe7S8+17.25O2+8H2O=3.5Fe2O3+8H2SO4 NiS+2O2=NiSO4 
Precious Metal ExtractionAu+0.75O2+4HCl=HAuCl4+1.5H2OPt+O2+6HCl=H2PtCl6+2H2OPd+0.5O2+4HCl=H2PdCl4+H2O
The recovery of precious metals from the PLATSOL™ process may be accomplished by a number of different routes. One route involves sequential reduction of any residual ferric sulphate present followed by reductive precipitation of precious metals on a synthetic copper sulphide precipitate, as shown below.
Ferric Reduction and Gold, Platinum and Palladium PrecipitationFe2(SO4)3+SO2+2H2O=2FeSO4+2H2SO4 2HAuCl4+3CuS+3H2SO4=2Au+3CuSO4+8HCl+3SH2PtCl6+2CuS+2H2SO4=Pt+2CuSO4+6HCl+2SH2PdCl4+CuS+H2SO4=Pd+CuSO4+4HCl+S
Similarly, the recovery of copper, nickel and cobalt from the precious-metal free solution may be accomplished by a variety of technologies, including copper solvent extraction—electrowinning, nickel and cobalt precipitation.